Out of curiosity, because it sounds like I'm doing something very similar and back when I was investigating it I saw no bias issues, what is the RIS trap? Is RIS conceptually flawed or is it a reoccurring 'gotcha' that you keep forgetting?

papaboo wrote:Out of curiosity, because it sounds like I'm doing something very similar and back when I was investigating it I saw no bias issues, what is the RIS trap? Is RIS conceptually flawed or is it a reoccurring 'gotcha' that you keep forgetting?

I used RIS for my light sources in the past: out of e.g. 1k lights, select 4 based on view independent information (i.e. brightness and area), then evaluate those four in more detail (including distance and orientation). This works like a charm until you need MIS. It is simply not possible to reproduce the probability of sampling a light explicitly when an implicit path reaches the light.

papaboo wrote:Out of curiosity, because it sounds like I'm doing something very similar and back when I was investigating it I saw no bias issues, what is the RIS trap? Is RIS conceptually flawed or is it a reoccurring 'gotcha' that you keep forgetting?

if you want to combine ris/mis have a look at the work of j. talbot and refs.

I guess I must do it slightly different then, because I just tested mine with MIS and MIS + 3 light RIS (or whatever warped self-rolled version of RIS I'm using) and there is no difference. I don't scale the PDF though when evaluating multiple light sources. I simply leave the light PDF as is and scale the contribution of the final selected light. That way my MIS weights should be fairly safe and independent of RIS.